<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
  </head>
  <body>
    <script>
      let years = prompt('请输入年份')
      let months = prompt('请输入月份')
      let day = 0
      switch (months) {
        case '1':
        case '3':
        case '5':
        case '7':
        case '8':
        case '10':
        case '12':
          day = 31
          break
        case '4':
        case '6':
        case '9':
        case '11':
          day = 30
          break
        case '2':
          if (years % 400 === 0 || (years % 4 && years % 100 !== 0)) {
            day = 29
          } else {
            day = 28
          }
          break
      }
      document.write(` 今年 ${years} 年, ${months} 月, ${day}天`)
    </script>
  </body>
</html>
